Aviation Week
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The U.S. FAA--nearly 12 years after the inflight breakup of TWA Flight 800--has issued a final rulemaking aimed at eliminating the risk of catastrophic fuel tank explosions.
Airlines, already staunching the flow of red ink, now face budgeting in the cost of retrofitting aircraft with the systems in the next decade.
The rule, long-awaited by the National Transportation Safety Board, is aimed at preventing another TWA Flight 800 accident. On July 17, 1996, Paris-bound Flight 800, a Boeing 747-131, broke up in flight shortly after departure from New York Kennedy (JFK) Airport, and all 230 people onboard were killed.
Investigators determined that the breakup was probably caused by the explosion of flammable vapors in the center wing fuel tank. The source of the ignition was never determined, but investigators thought it likely that wiring in the fuel quantity indication system caused a short circuit.
Since that day, the reduction of fuel tank flammability has been on the NTSB's Most Wanted List of safety recommendations. The FAA issued 70 advisory circulars and 100 airworthiness directives aimed at mitigating risks, most of which aimed at reducing sources of ignition.
In May 2001, the agency issued SFAR 88 (Special Federal Aviation Regulation) aimed at preventing ignition sources, but did not issue a proposed rule until November 2005.
The July 16 final rule follows the proposed rule, with some exceptions. It would require Boeing and Airbus passenger aircraft with heated center wing tanks (HCWT) and manufactured before 2009 to be retrofitted with a flammability reduction means (FRM), such as a fuel tank inerting system, or ignition mitigation means (IMM), such as polyurethane foam. (A fuel tank inerting system replaces oxygen in a fuel tank with an inert gas, such as nitrogen, to reduce risk of flammability. For the full 223-page rule, go to http://federalregister.gov/OFRUpload/OFRData/2008-16084_PI.pdf
In addition, the rule requires that an FRM or IMM be installed on passenger and cargo aircraft with HCWTS manufactured in the 2009-2017 period. Boeing 717, 727 and certain 767 and 777 aircraft, as well as Airbus A321, A330-200 and A380 aircraft, are excluded.
Cargo aircraft are excluded from the retrofit requirement. However, If an FMM/IMM-equipped passenger aircraft is converted to cargo aircraft, the cargo operator would be required to keep the system operational.
The FAA estimates total compliance cost of the rule at $1 billion, $975 million for air carrier passenger aircraft and $37 million for production cargo aircraft, over a 35-year period.
The final rule indicates that 2,732 passenger aircraft would require retrofit, with kit costs ranging from $77,000 to $192,000, depending on aircraft type. Total retrofit costs would run $110,000 to 250,000 per aircraft, costs that, over time, would decline $10,000-17,000, according to the FAA.
In addition, 2,290 production passenger aircraft and 88 production cargo aircraft manufactured in 2009-2017 will be affected by the final rule.
Photo of Flight 800's reconstructed TWA 747: National Transportation Safety Board, via Skybunny at Wikipedia



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